MODERN BIOLOGY 433 



Pasteur denies spontaneous generation 

 Pasteur began his researches in the purely chemical sphere; he investigated 

 organic acids, chiefly the isomeric, and he obtained valuable results in con- 

 nexion therewith. Thence he was led to study the question of the molecular 

 structure of sugar and the manner in which this substance is converted into 

 different isomeric alcohols and acids — in other words, into the process of 

 fermentation. His first experiments in this field were concerned with the 

 formation of lactic acid; he found on the surface of sour milk minute greyish 

 spots, which he examined microscopically and experimentally. Under the 

 microscope they appeared as a mass of minute globular formations, smaller 

 in size than those of which ordinary yeast is composed; when placed in a 

 saccharine solution they at once disintegrated it into lactic acid. Without 

 at the moment drawing any conclusion as to their origin, he maintains that 

 all fermentation is caused by similar minute organisms. If we plant out such 

 organisms of a definite type in a saccharine solution, wt get a definite form 

 of fermentation: alcoholic fermentation, br.tyric-acid formation; if, on the 

 other hand, a suitable saccharine solution is allowed to stand by itself, there 

 are set up a number of simultaneously disintegrating processes induced by 

 different organisms operating at the same time. 



It goes without saying that the chemists of the old school did not feel 

 that they had much to gain from these new discoveries. They at once found 

 a keen supporter in Felix Archimede Pouchet (1800-71), professor at Rouen, 

 who was reputed both as a botanist and as a zoologist. In a series of investi- 

 gations he tried to prove that the micro-organisms arising upon fermentation 

 and putrefaction are spontaneously generated, and this owing to the very 

 fact of those chemical changes; the fermentation forms the initial stage of 

 the process whereby living creatures arise from the decomposition of existing 

 organic substance. In the view of such a theory Pasteur's fermentation experi- 

 ments were, of course, pure irrational nonsense, and thus began a lengthy 

 controversy betw^een these two experimental scientists, in which the scientific 

 world and eventually the enlightened public became keenly interested. 



Controversy between Pasteur and Pouchet 

 To Pasteur the specific character of the different fermentative organisms was 

 in itself a proof that they are not the product of chemical change, but actual 

 species of living beings , which come into existence through the multiplication 

 of existing individuals. But whence, then, come all those different organisms 

 which immediately populate saccharine solutions that are allowed to stand, 

 and food that is kept too long? Schwann had derived putrefaction from the 

 air, and Pasteur endeavoured to prove this by experiment; he filtered air by 

 sucking it in through a tube filled with cotton-wool, thereby obtaining a 

 collection of dust particles, which were transferred with great care to a 

 retort filled beforehand with boiled and cooled saccharine solution; the neck 



